Aerogels are low density solids typically made from gels which are dried in such a way as to preserve the gel structure. On account of the fact that they possess high porosity with very small, nanoscale pores, aerogels have many interesting properties, including low thermal conductivities, low dielectric constants, and high surface areas. These properties make aerogels highly desirable for many applications such as insulation for aerospace, construction, pipelines, refrigeration, electronics and clothing or as low dielectric substrates for lightweight antennas and other devices.
On account of their low density and open porosity, aerogels can also be fragile and environmentally sensitive, making their utilization difficult in certain applications. As such the mechanical properties of aerogels are density dependent, generally decreasing with decreasing density. This is in contrast to the desirable properties of aerogels (e.g. porosity, light weight etc.), which are improved with decreasing density. Thus, a way to improve the mechanical properties of aerogels especially at the low densities is highly desired.
Polymer aerogels, especially polyimide and polyamide aerogels, have improved mechanical properties over silica or silica-polymer hybrid aerogels. They also can be made in flexible thin films, increasing utility in many applications. However, the mechanical properties of these polymer aerogels still decrease with decreasing density. In recent years, cellulose nanocrystals (CNC) have been investigated as, potentially low cost, biorenewable reinforcement for polymers. They exist in most plants and can also be found in the mantles of sea tunicates and obtained from certain algae and bacteria. Their surface functionalities can be easily modified with different charge densities or surface functionality, making them compatible with many types of polymers. CNC/polymer nanocomposites also have been shown to respond to stimuli as a new class of smart materials.
As stated, mechanical properties of the polyimide polymer aerogels decrease as density is decreased. In addition, thin films from very low density formulations are especially weak and difficult or impossible to fabricate.